No1=1
No2=2
1、 let result=No1+No2 let No1++ let No1+=3
2、 result=$[No1+No2]
3、 result=$((No1+No2))
4、 result=`expr $No1 + $No2` # '$' and space are necessary.
5、 echo "$No1+No2"|bc
echo "scale=3; 3/4"|bc #keep three decimal places
echo "obase=2; ibase=10; 100"|bc #Convert decimal to binary.
echo "sqrt(100)"|bc
echo "10^5"|bc